Introduction

Grocott kit is used in histology for visualization of fungi, certain pathogens, basal membranes and histology argentaffin structures in general. The staining procedure starts with the periodic acid solution being used to oxidize 1,2-glycols to aldehydes. During incubation in silver-methenamine-borate working solution aldehydes are reduced and at the same time silver ions are reduced to a metallic silver that manifests as brown to black structures on the section. This is followed by toning with the gold chloride solution that additionally improves the staining intensity of target structures (fungi, basal membranes and others), and it reduces background staining. Excessive unbound silver-gold bonds are removed by rinsing the section with the sodium thiosulfate solution. Finally, the sections are exposed to Fast Green F.C.F. dye that stains background structures; that, in turn, creates clear and visually reach contrast to target structures (colored in brown to black).